1. Field of the Invention
The present invention relates to a stretch film. In particular, the present invention relates to a stretch film product for palletizing.
2. Description of the Prior Art
For packing or wrapping pallets, bales of straw, fruit etc. it is known that perforated plastic stretch films are used in order to provide sufficient stretchability of the packaging film as well as ventilation of the products to be packed. Known from EP 0 820 856 A1 is a pre-stretched plastic stretch film in which holes are formed by a thermal irradiation method without contacting the film and thus without waste of film material, for example, caused by punching out holes.
Known from EP 0 909 721 A1 is a perforated extensible palletizing film comprising a longitudinally elongated thin sheet of extensible plastics provided with ventilation holes and longitudinal reinforcement elements which are made of extensible plastics and are adapted to increase the strength of the film in the pulling direction.
Similar perforated stretch films are known from WO 01/60709 A1 and WO 02/094674 A1.
The perforations of these stretch films represent a macro perforation in which holes having a diameter of at least 5 mm are provided in a base film. Films with significantly smaller perforations represent a micro perforation and are irrelevant to the present invention.
The above should not be confused with film products on which slits or small punctures have been made initially with the intention that these increase, break or open (resulting in large openings) as a result of the film being stretched during usage in a wrapping machine with a prestretching system.
In practice, a number of problems may arise in connection with the above-described macro-perforated stretch films comprising reinforcing elements. Namely, the stretch films are normally used by automatic or semi-automatic stretch wrapping machines, for example, in order to wrap products stacked on pallets. To ensure good material utilization, it is desirable to stretch the stretch film during the wrapping operation by e.g. 100 to 250% as compared to the stock of film material still on a winding drum. To this end, considerable force is required which can be significantly increased by reinforcing elements fixed onto the stretch film, so that in the end the wrapping machine, under special conditions, is no longer capable of providing sufficient stretching of the stretch film for lack of sufficient power.
On the other hand, if the wrapping machine is strong enough to provide the desired stretching, there is the danger that the forces acting on the products to be wrapped are too great. If the products are, for example, boxes, there is the risk that the stretch film and/or the reinforcing elements fixed thereto, press the products or their packages together and damage them.
Further there is the danger that the additional reinforcing elements have not been fixed onto the base film by the manufacturer with sufficient reliability. In this case the respective reinforcement element which, for example, is formed as an elongated plastic film strip, can detach itself from the carrier film and become engaged in a nip roll of a wrapping machine, thereby obstructing the film feed path.
In addition, it has been found in the case of the films known from the prior art that the respective carrier films or base films hardly contributes to strength. Basically, they serve rather only to carry the reinforcement elements, which predominantly ensure the desired strength. Accordingly, the material of the base film is utilized insufficiently.
The reinforcement elements fixed onto the base film may convey to the observer an impression of poor optical properties and poor appearance of a pallet wrapped in the stretch film, thereby detracting from the overall impression of the pallet and the valence of the products stacked thereon.